System and method for lighting control network recovery from master failure

ABSTRACT

The present invention provides a master-slave architecture for a radio frequency RF networked lighting control system having all slave elements (ballasts) configured as backups for a network master control unit. In the system and method of the present invention a slave element can become the network master network unit without reconfiguring the network and without any human intervention. Similarly, both a master and one or more slave elements may recover from a temporary outage without necessitating reconfiguration of the network and without any human intervention.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application Ser.No. 60/433,750 filed Dec. 16, 2002, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is related to recovering the ballast control in awireless lighting control network when the main controller (master)fails. More particularly, this invention is related to a wirelesslighting control network system and method in which all lightingballasts act as backups for a network master control unit. Mostparticularly, this invention is related to a system and method for amaster-slave architecture for a wireless lighting control network thatinclude all lighting ballasts as backup for a network master controlunit such that there is no need for reconfiguration of the network orhuman intervention when a master fails or functioning of the master orslave ballasts is interrupted.

2. Description of Related Art

Traditional lighting has wall switches wired to the ballastsindividually or in groups. If one of the switches fails, the ballaststhat are controlled by other switches won't be affected. In wirelesscontrol, the on/off or light intensity is controlled by the signalstransmitted from a remote table-top or handheld control unit viainfra-red (IR) or radio frequency (RF) communication media.

There are basically two types of system configurations in wirelesscontrol. One is a distributed system that has several remote controlunits, each remote unit controlling a certain number of ballasts throughthe wireless links. The ballasts obtain the IDs of their designatedcontrollers during the initialization of the system. Then, during normaloperation the ballasts “listen” and react to the lamp operationalsignals coming transmitted by these controllers. The systems describedin U.S. Pat. No. 5,848,054 to Mosebrook et al. and U.S. Pat. No.6,174,073 to Regan, fall into this category.

The other type of system is a master-slave oriented networkedarchitecture, which is the focus of this invention. There is one centraldevice, so called “master” or “network coordinator” that managescommunication among the network nodes. The ballasts and the remotecontrols both act as the slaves in the network. All the informationabout the wireless links between the keys on the remote control and theballasts is gathered in a table stored in the master during initialconfiguration of the system. During the normal operation, the signaltransmitted by a remote control is routed to its destination ballast bythe master based on the link information in the table. The physical formof the master can be the same as a slave device, i.e. the master canreside in the remote control or the ballast. It is preferable to put themaster in the ballast as it is mains-powered and at a fixed location.Connecting to the mains allows the master to transmit beacon packetsthat contain the master status information as a way to keep the slavesin touch every once in a while. Being at a fixed location avoidsproblems a missing handheld remote control since all the networkinformation is lost in such a case.

The master-slave networked system has the following advantages over thedistributed system:

-   -   If more than one remote-control is needed in a multi-zone        office, a separate master is essential for network recovery if a        remote control is lost.    -   A master-slave architecture centralizes the control information        for the local network and makes it easier to form the        building-wide network.

In both wireless systems, there could be several reasons for a systemfailure:

-   -   Power Loss: In normal operation, the ballasts should not be cut        off from the mains power for any reason, as they have to keep        the RF communication alive all the time. Turning-off the lamps        only puts the lamp-drivers in stand-by in digital ballasts, and        it does not shut off the power supply to the circuits. Sometimes        the controller that happens to be installed on a different mains        power line from the ballasts experiences a power outage. Other        times the controller could be running out of battery if battery        powered.    -   Circuit malfunction: This includes circuit failures in the        master control unit (MCU) or RF transceiver, and the temporary        RF signal blockage/shielding or interference such that the        communications between the devices are blocked.    -   Master Control Unit Failure: In a wireless network the master        control unit represents a single point of failure. That is, once        the master fails, all link information kept only by the master        is lost. In a point-to-point network the network is no longer        operable. This also occurs because the master routes all the        packets and the master fails.

There are several ways to enhance the reliability. The wireless systemtaught by U.S. Pat. No. 5,848,054 to Mosebrook et al., increases thereliability communications by adding repeaters between the source anddestination devices. When the master and the ballasts suffer fromintermittent communication in the direct path due to distance or RFinterference, a repeater provides an additional communication path.However, this does not solve the problem of the master going completelydead.

Another system, taught by EP0525133 to Edwards et al., solves the masterpower outage problem by providing a battery as a back-up power source.When AC power is available, the battery is being charged. When the AC iscut off, the power supply automatically switches to the battery. Eventhough this idea teaches a battery backup for conventional hardwiredlighting systems, it can be applied to the wireless system too. However,it can be costly to provide an additional power supply to every controldevice.

In a master-slave networked system, due to the important role of themaster, it is critical to make sure that there is always a masterworking properly at all times. If the controller fails due to a poweroutage (dead battery) or malfunction, the problem arises of to how toregain controls of the ballasts. New replacements can be brought in, butthe configuration, such as which key to control which ballasts, has tobe set up again since there is no hardwiring in a wireless controlsystem. Depending on how the wireless control network is built in thefirst place, sometimes this may mean starting the configuration fromscratch all over again.

SUMMARY OF THE INVENTION

The present invention solves the problems associated with a singlemaster, as discussed above, by providing multiple back-up masters in amaster-slave orientated control network. The system and method of thepresent invention enhances system reliability without an extra device orcostly circuitry. Each ballast in the network has the potential to be amaster when needed. This means each device needs a little bit of extramemory to store the master program. In a digital ballast, the cost foradditional memory is minimal.

The master malfunction is automatically detected by the slaves in thenetwork. Once a master fails, a back-up master takes control of thenetwork following a pre-established protocol or algorithm of a preferredembodiment. The network recovery takes place automatically and istransparent to the end user. There is no need to set up the networkcontrol configuration again.

The original master resides in one of the ballasts after theinstallation and configuration of the network, which includes thephysical installation, registration of the ballasts with the networkmaster (so called “enumeration”), and associating the ballasts withcertain buttons on the remote control (so called “binding”).

All the ballasts (slaves in the network) have the possibility andcapability of becoming the new master if needed. It is randomly decided,when necessary, which ballast is the next back-up master. There is nopriority number assigned before hand.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart of the back-up master operation takingover control of the network.

FIG. 2 illustrates the failure of a network master control unit andseveral slaves of the same wireless lighting network.

FIG. 3 illustrates recovery of a network master control unit from apower outage.

DESCRIPTION OF PREFERRED EMBODIMENTS

The wireless lighting control network functions analogously to awireless communication network. The lighting network itself isidentified by a network ID, which is the essential information forcommunication among all the network nodes and there is a several layercommunication protocol stack associated with every component of thewireless lighting network. After the network is established by themaster and an enumeration of the lighting elements and pairing ofenumerated lighting elements with keys are done, the master has all thepairing information stored in a pairing-link table in the protocolstack. Each pairing-link table entry specifies which ballast(s) reactsto which key and on which remote control. The master transfers thispairing-link table to all the slaves in the network. Every time thepairing-link table is changed, the master keeps all the slaves updated.

Master and slaves exchange status information at pre-determinedintervals to make sure that the master is working properly. The mastersends out beacon packets that contains status information at thesecertain intervals. The slaves receive the beacon packets and determinethe state of the master. As illustrated in FIG. 1, at step 11 slavesalso wake up a master that is in its sleep mode at intervals t₁. Eachslave keeps in touch with the master with the same interval but at adifferent point of time (based on a randomly generated number).

Once a slave finds that the master is not working, at step 13 it waits acertain delay time t₂ before taking any action in case the master becomeoperational again. Once the delay is timed out, at step 15 the firstslave who discovers the master-failure will start to convert itself tothe new master. While the first slave is waiting, the rest of the slavescan find out the master-failure too, but all of them have to wait forthe same delay t₂ before reacting, so the first to discover the masteroutage becomes the new master.

The new master switches to the master status using the master code thathas already been stored in its memory.

The new master establishes the network using the same network ID thatthe previous master used, providing this network ID is not used by anyother networks in the vicinity. Then the application layer of the masterdoes the following, as shown in FIG. 1.

-   -   1. Informs the lower layers in the new master to act as a master        (sending beacons . . . ) using the same network ID.    -   2. At step 15 informs the slaves that a new master is taking        over the network and they should synchronize with the new master        in terms of listening to the beacons and checking the master's        status.    -   3. At step 16 updates the pairing-link table and transmits a        copy of it to all the slaves.

The algorithm of the present invention can be implemented in combinationwith a wireless communication protocol, either proprietary or openstandard to ensure a reliable RF communication such as Zigbee™. Zigbee™is a low cost, low power consumption, two-way, wireless communicationsstandard aimed initially at automation, toys, & PC peripherals, and is agood candidate for implementing this system and method of the presentinvention for a recoverable RF wireless lighting control network thatuses slaves as backup masters.

Normal Operation

The very first time the system is installed, the master and slaves alltake on the physical format of a ballast. In a preferred embodiment,their roles are distinguished by certain mechanisms or algorithms. In agiven single room, there must be a master and at least one slave. Allthe devices, including master and slaves, have nonvolatile memories(NVM) to store the enumeration status information, network IDinformation and pairing-link table information. When the devices areinitially powered up, the master checks its NVM to see if it has been inany network as a master before. If not, it establishes its network usinga randomly generated network ID. The slaves check their NVMs to see ifthey have been in any network as a slave before, if not, they try toenumerate to a master available in their RF vicinity. Once they areconnected to a master, the lamp flashes to provide feedback to the userand the user presses a button on the remote control to confirm that itshould be included in the network. The remote control is also a slave tothis network and has to be connected to the master before the ballasts.

Reasons for Master Failure

There are two major reasons for the master to fail:

1. Power Loss: During normal operation, both master and slave must notbe cut off from the main power supply for any reason, as they have tokeep the RF communication alive all the time. Turning off the lamps onlyputs the lamp drivers in stand-by, and it does not shut off the powersupply to the circuits. When the ballasts are initially powered up fromthe main power supply, if a ballast is supposed to be a master, itstarts to establish its network. If it is supposed to be a slave, itstarts to request joining a network. The ballasts store their IDs andnetwork connection information (such as the pairing-link table, the flagindicating if it has been enumerated before, etc.) in the non-volatilememory so that the network connection can be recovered after a temporarypower interruption. If the power of the whole system is consistentlyinterrupted, then the ballasts maintain their previous roles after thepower comes back. In this case, the power-up reset does not trigger theenumeration request in the ballast if it was already in a networkpreviously. This scenario is not considered a master failure since thewhole network recovers to its previous state before the powerinterruption without further procedures being invoked.

However, sometimes the master could be installed on a different mainpower line from the slaves. When its power is experiencing an outage andthe one for the slaves is not, a back-up master is needed to keep therest of the slaves under control.

2. Circuit malfunction: This includes failures in the MCU or transceiverand temporary RF signal blockage/shielding around the master, etc. Inthis case, a back-up master is also necessary to recover the operationof all the slaves.

FIG. 2 illustrates the master failure situation. If a circuitmalfunction occurs and the network master control unit 22 is notfunctional, a new master control unit 28 takes over control of theexisting lighting network by following the algorithm illustrated inFIG. 1. By way of example only, several slaves and a network mastercontrol unit 22 are shown in a non-working circuit in FIG. 2. The newnetwork master control unit 28 takes control of the exiting lightingnetwork 20, updates its pairing-link table to reflect these non-workingunits and transmits the updates to all the working slaves in thenetwork.

Disabled Master Coming Back

In the case that the previous master recovers from its temporary RFblockage or power outage, it tries to join the same network again, butnot as a master, instead, as a slave since there a new master hasalready taken over control of the network. The following describes thetwo different situations where the previous master recovers from atemporary power outage and RF blockage. If the previous master failureis due to circuit malfunction, it cannot recover anyway.

1. Coming Back from Temporary Power Outage

Referring now to FIG. 3, when the previous master regains power 31, itgoes through the power-up reset and then checks the contents of its NVM.When its NVM indicates that it was previously the master of a network34, it tries to recover its role as master in the same network byattempting to establish its network using the same network ID 34. Itstarts the search at this particular network identifier, and thenlistens for a beacon packet to see if anyone else is already using thisnetwork ID 35. As soon as it finds out that another device has alreadytaken its place as the master in this particular network (using theprevious network ID), it withdraws itself from attempting to become themaster again, and it enumerates to the network as a slave 36. Since thenetwork ID is still the same, it does not require any user interventionduring the enumeration.

As can be seen in FIG. 3, some of the slaves might have been out ofpower, as well, if they were on the same power line as the previousmaster. When they regain power, they go through power-up reset and thencheck the contents of their NVMs. As their NVMs indicate that they werewas previously slaves of a network, they try to recover this role as athe slave 36, in the same network by attempting to enumerate using theprevious network ID. The new master is able to accept them without userintervention since the new master has the information that the slave hasbeen in this network before the power was out.

2. Coming Back from Temporary RF Communication Blockage

When the previous master failure is due to the temporary RFcommunication blockage, the protocol stack is able to report thisproblem to the application layer. The application layer then goes backto the beginning of the routine, which is power-up reset. Then it keepstrying to re-establish its network using the same network ID 38. If, bythe time the RF channel is clear for communication for this device, thenew master has already taken over the network, the old master withdrawsfrom trying to become the master, but tries to become a slave, which isthe same as the situation in coming back from temporary power outage andis discussed above and illustrated in FIG. 3. If by the time the oldmaster regains RF accessibility, the new master has not yet takencontrol of the network, the old master recovers control over the samenetwork with the same ID and this is illustrated in FIG. 3.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will be apparent to those skilled in the art. The presentinvention, therefore, should be limited not by the specific disclosureherein, but only by the appended claims.

1. A lighting control network recovery system for a wireless network oflighting elements, comprising: a plurality of ballasts, each ballast ofthe plurality of ballasts being configurable as one of a slave elementand a network master control unit; wherein one ballast is configured asthe network master control unit to control each ballast that isconfigured as a slave element, and, when the network master control unitis no longer in communcation with one or more of the ballasts, one ofthe ballasts that is configured as a slave unit is configured to be thenetwork master control unit.
 2. The system of claim 1, including: atleast one remote control unit having a plurality of keys; and at leastone main power line having the ballasts connected thereto such that: theone of the ballasts that is configured as the network master controlunit is adapted to setup the network configuration of the lightingcontrol network by recording a registration of each association of atleast one key of the at least one remote control to at least one of theballasts to control the at least one ballast thereafter.
 3. The systemof claim 2, wherein the at least one remote control unit is configuredas a slave element that is connected to the network master control unitbefore any of the plurality of ballasts that are configured as a slaveelement.
 4. The system of claim 2, wherein: each ballast includes anon-volatile memory, a pairing-link table is stored in the non-volatilememory of the ballast that is configured as the network master controlunit to record a registration of each ballast that is configured as aslave element that registers with the network master control unit, andeach binding of the ballasts in the pairing-link table with at least oneof the plurality of keys of the at least one remote control unit, andthe ballast that is configured as the master control unit is configuredto transmit the pairing-link table to each other ballast each time thepairing-link table is modified by the network master control unit, forstorage in the non-volatile memory of the ballasts.
 5. The system ofclaim 4, wherein: the ballast that is conficiured as the master controlunit is configured to periodically transmit a beacon packet, and theballasts that are configured as the slave element are configured suchthat a first ballast that fails to receive the beacon packet: waits agiven delay time, configures itself as the master control unit, using asame network ID and the pairing-link table in its non-volatile memory,and notifies the other ballasts of its reconfiguration as the mastercontrol unit.
 6. The system of claim 2, wherein the ballast that isconfigured as the network master control unit is configured to:determine whether an other ballast has become configured as the mastercontrol unit, and to configure itself as a slave element and registerwith the other ballast if the other ballast has been configured as themaster control unit, determine whether network communications have beenlost and reestablishing the network if the other ballast has not beenconfigured as the master control unit.
 7. The system of claim 6, whereinthe system is implemented using a low power consumption, two-waywireless communication standard having a protocol and comprising aradio, a physical layer, a data link layer, and an application layer. 8.The system of claim 7, wherein the two-way wireless communicationstandard is Zigbee™ and the protocol is Protocol for Universal RadioLink (PURL).
 9. The system of claim 6, wherein the ballast that isconfigured as the network master control unit determines whether theother ballast has become configured as the master control unit each timethe ballast is powered on.
 10. The system of claim 1, wherein theballasts that are configured as slave elements are configured totransmit wake-up calls to the ballast that is configured as the networkmaster control unit.
 11. A method for recovery control of a wirelesslighting control network in which a master ballast is configured tofacilitate communication of commands from a plurality of controlelements to a plurality of ballasts based on a pairing-link table thatincludes a plurality of associations between control elements andballasts in the network, comprising: communicating the pairing-linktable from the master ballast to each of a plurality of slave ballasts,monitoring, at each of a plurality of slave ballasts in the network, foran indication that a master ballast is present in the network, and if afirst slave ballast of the plurality of slave ballasts fails to receivethe indication within a given period of time, configuring the firstslave ballast to become a new master ballast in the network, andfacilitating communication of commands from the control elements to theballasts via the new master ballast, based on the pairing-link tablepreviously received by the new master ballast.
 12. The method of claim11, wherein the control elements include keys of at least one remotecontrol unit: configuring the lighting control network by: registeringeach slave ballast with the master ballast, and associating eachregistered slave ballast with at least one of the keys; and controllingthe lighting control network by the keys, via the master ballast. 13.The method of claim 12, including registering the at least one remotecontrol unit as a slave element with the master ballast beforeregistering each slave ballast.
 14. The method of claim 12, including:initializing the pairing-link table at the master ballast as empty;enumerating each slave ballast that registers with the master ballast inthe pairing-link table of the network master control unit; associatingeach slave element enumerated in the pairing-link table with at leastone of the keys.
 15. The method of claim 14, wherein the configuring ofthe first slave ballast to become the new master ballast includes: whena master code is already stored in the memory of the new master ballast,establishing a network with the same network ID that the master ballasthad used; informing each slave ballast to monitor for an indication thatthe new master ballast is present on the network; updating thepairing-link table of the new master ballast; and transmitting theupdated pairing-link table to each slave ballast.
 16. The method ofclaim 12, including, on power-up reset: at the master ballast:determining whether the network has been established, and if the networkhas not been established, establishing the network; otherwise, if thenetwork had previously been established determining whether the networkis already in use, and if the network is already in use, enumerating theballast as a slave element to a new master ballast; otherwise, if thenetwork had been established but is not already in use, reestablishingthe network based on its stored pairing-link table; and at each slaveballast: determining whether the network has been established, and ifthe network has not been established, reconfiguring itself to become amaster ballast and establishing the network; otherwise rejoining thenetwork.
 17. A system with a low power consumption, two-way wirelesscommunication standard having a protocol and comprising a radio, aphysical layer, a data link layer, and an application layer thatperforms the method of claim
 16. 18. The system of claim 17, wherein thetwo-way wireless communication standard is Zigbee™ and the protocol isProtocol for Universal Radio Link (PURL).
 19. The method of claim 16,wherein determining whether the network has been established is based onwhether a network identifier is stored at the ballast.
 20. The method ofclaim 12, including transmitting wakeup calls from the slave ballasts tothe master ballast.